In some satellite positioning system receivers (SPS) also referred to herein as global positioning system receivers (GPS), for example, battery-operated portable NAVSTAR GPS receivers, designers must consider a tradeoff between power consumption and operation of the SPS engine. In SPS based navigation applications, for example, battery power consumption depends on the rate or frequency at which the SPS engine computes pseudoranges and generates positioning, heading, speed and other information for the navigation application. In many SPS receiver applications, including some navigation and routing applications, the SPS engine must generally operate relatively continuously to provide the accuracy and performance expected by consumers. This sustained operation consumes power and may require the allocation of substantial computational resources, one or both of which may be in limited supply.
U.S. Publication No. 2003/0236619 entitled “Low Power Position Locator” discloses a device for determining user position including a GPS receiver that intermittently determines a reference position at a relatively low frequency duty cycle to reduce power consumption. In U.S. Publication No. 2003/0236619, a user's current position is determined using the reference position and change information relative to the reference position detected by a comparatively low power consumption inertial sensor system. In one embodiment of U.S. Publication No. 2003/0236619, the duty cycle of the GPS received is fixed, and in another embodiment the duty cycle is variable depending upon whether the change in position detected by the inertial sensor system exceeds a specified limit.
U.S. Pat. No. 5,731,978 entitled “Method And Apparatus For Enhancing Vehicle Navigation Through Recognition of Geographical Region Types” discloses a vehicle navigation system capable of altering parameters of a navigation algorithm based on changes in the geographical region, for example, changes indicated by the digitization density of a map database, where the vehicle is located. The navigation system of U.S. Pat. No. 5,731,978, for example, provides extra user guidance in hilly terrains and eliminates extraneous maneuvers in densely populated areas. U.S. Pat. No. 5,731,978 also discloses adjusting the size of search regions employed to identify position possibilities based on the density and regularity of the layout, for example, street grids, in the map database.
The various aspects, features and advantages of the disclosure will become more fully apparent to those having ordinary skill in the art upon careful consideration of the following Detailed Description thereof with the accompanying drawings described below.